1) Field of the Invention
The present invention relates generally to agricultural implements with hydraulic depth control, and, more specifically, to an improved depth control adjustment for such an implement.
2) Related Art
Implements such as field cultivators and chisel plows include frames supported for vertical movement by depth control wheels. The depth control wheels are carried on a rockshaft and raised or lowered relative to the frame by a hydraulic cylinder connected between the rockshaft and the frame. Often, a depth control valve is connected between the cylinder and the hydraulic system on the tractor. A linkage connected to the rockshaft operates the valve to maintain a preselected frame height which, in turn, establishes a given working depth for the tools carried by the frame. Current control systems which work off the rockshaft have problems maintaining repeatability, largely because of the slop in the bearing blocks that mount the rockshaft. In addition, depth indications are usually only relative and do not provide a gauge of absolute depth setting.
Various attempts to control depth directly from cylinder extension have often resulted in relatively complex and expensive devices. Chains or other flexible member devices have been used to gauge cylinder extension, but maintaining the flexible member taught under all conditions has been a continuing problem.
Other types devices are available to limit retraction of a cylinder to set working depth, including donut-shaped spacers placed over the cylinder rod or cylinder-mounted valves. However, most of these devices suffer from one or more disadvantages, such as inaccessibility and limited adjustment capability.